Why volume matters
Price tells you what happened; volume tells you how many people agreed. A breakout on two or three times the normal volume is more likely to be backed by real buying than one on light volume, and a heavy-volume sell-off often marks distribution by large holders.
- Volume × is the latest day’s volume divided by the average of the previous 20 days.
- Up / down on heavy volume combines a 1.5× or larger volume day with a gain or a loss.
- Unusually quiet lists stocks trading under half their normal volume: often a pause before the next move.
- $ volume is average daily volume times price: how much money changes hands each day.
During the trading day the latest day is still in progress, so volume ratios start low in the morning and climb into the close.
Frequently asked questions
Does relative volume adjust for the time of day?
No. It compares the volume so far today with full-day averages, so early in the session most ratios are below 1×. The lists are most meaningful near or after the close.
Why do I need an Alpaca key?
US stock prices are licensed data, so they can’t be handed out for free by a website. Alpaca gives anyone a free market-data key that allows 200 requests a minute and returns many stocks per request, which is enough to scan the whole list. Your key is saved only in your browser and is sent only to Alpaca. See how to get a free Alpaca key.
Which stocks does it scan?
About 600 US stocks and ETFs: roughly the S&P 500, popular growth and momentum names, and around 75 of the most traded ETFs. The largest 135 load first; the rest follow automatically a few seconds later.
Is the data real-time?
Alpaca’s free data is 15 minutes behind the market. Daily figures update through the trading day, and the latest candle is the current (unfinished) day while the market is open.